Integrated servo actuator

ABSTRACT

An integrated servo actuator including in a single package a force motor, a fluid modulator controlled directly by the force motor, and an actuator movable in response to the characteristic flow of fluid through the modulator. An integral potentiometer mounted in the housing produces a signal which is a function of the actuator position.

D United States Patent 11 1 1111 3,729,133 McCormic 1 1Marcl1 13, 1973541 INTEGRATED SERVO ACTUATOR 3,464,318 9 1969 Thayeretal. ..9l/3633,516,331 6/1970 Oelrich et a1 ..91/41 [75] Inventor Jseph MccmmwPawlmg' 3,521,535 7 1970 Oelrich ..91 361 [73] Assignee: DeltaHydraulics, Incl, Braintree,

' Mass Primary Examiner-Paul E. Maslousky [22] Filed: March 17, 1971AttrneyWolf, Greenfield & Sacks [21] App]. No.: 125,333

Related US. Application Data [57] ABSTRACT Continuation of Ser No 808749 March 20 1969 An integrated servo actuator including in a singleabandoned package a force motor, a fluid modulator controlled directlyby the force motor, and an actuator movable 52 us. (:1. ..91/47, 91/363R, 91/417 R in response to the characteristic flow of fluid through 51Int. Cl. ..Flb 13/16, FlSb 15/17 the modulfltot- Ahihtegtalpotentiometer mounted in [58] Field of Search.....9l/52, 363, 47, 386,361,417 the housing Produces a Signal which is a function of theactuator position. [56] References cued 9 Claims, 3 Drawing FiguresUNITED STATES PATENTS 2,789,543 4/1957 Popowsky 91/386 3,430,536 3/1969Oelrich ..91/47 IO 22 52 54 e a so 1 1a 38 M x 64 v m 20 2 E b e i l6 0/1\ A 1 36 \X\\\ L ee 9e as 62 73 92 PATEINTEDMARISIBYS 3,720,118

sum 20? 2 CONTROLLED ATM.

FIG. 2

SET POINT INVENTOR. JOSEPH Mc CORMI CK QWWMMM ATTORNEYS INTEGRATED SERVOACTUATOR This application is a continuation of application Ser. No.808,749, now abandoned, filed Mar. 20, 1969.

This invention comprises a new and improved integrated servo actuator.

At the present time in order to achieve the function performed by thepresent invention, three separate and physically unrelated elements arerequired; namely, a force motor, some form of hydraulic converter, and afinal control element. These separate devices must be specially matched,are expensive, and occupy a considerable volume.

One important object of this invention is to integrate the variouscomponents of a servo actuator control into a unitary structure.

Another important object of this invention is to dynamically couple theseveral elements of a servo actuator control to increase the speed ofresponse and eliminate play or backlash which is necessarily presentwhen the various parts in a linked system are physically separated.

And another important object of this invention is to provide anintegrated servo actuator which may be modified or changed to achievedifferent gain combinations as desired for the particular application inwhich the unit is used.

To accomplish these and other objects the integrated servo actuator ofthis invention includes in a single housing a force motor, a modulator,and an actuator which are dynamically coupled together and cooperatewith one another directly. Thus, a control signal may be fed to thedevice and internally the unit converts the signal to a mechanicaldisplacement, and in turn to a pressure or flow valve, and finally to amechanical displacement of a different order of magnitude as the controlactuation. In the preferred form of this invention, the servo actuatorincludes an integral position feedback element which allows the unit toprovide closed loop control.

These and other objects and features of this invention along with itsincident advantages will be better.

understood and appreciated from the following detailed description ofone embodiment thereof, selected for purposes of illustration and shownin the accompanying drawing, in which:

FIG. 1 is a cross sectional view of an integrated servo actuatorconstructed in accordance with this invention;

FIG. 2 is a diagram showing one application of this invention; and

FIG. 3 is a diagram showing another application of this invention.

The integrated servo actuator shown in the drawing generally includesthree stages; namely, a force motor 10, a modulator element 12, and aservo actuator 14. An integral position feed back assembly 16 isdisposed in the servo actuator. These various components are describedin detail below.

The force motor assembly is disposed in a cap 18 and includes inner andouter pole pieces 20 and 22 whichtogether define a gap 24 in which islocated a bobbin 26. The bobbin includes a collar 28 about which coil 30is wound, and a spring 32 supports the bobbin 26 for axial motion in thegap 24 as the coil 30 moves in response to its energization. Anelectrical conduit may be connected to the cap 18 by means of thecoupling 34, and the leads which control the energization of the coil 30extend through the coupling 34 and the passage 36 to the coil 30. Thedisplacement of the coil 30 with bobbin 26 is directly proportional tothe excitation of the coil acting against the supporting mechanicalspring 32.

The bobbin 26 also carries a null screw 38 which controls the dischargethrough orifice 40 of the modulater 12. It is evident from an inspectionof the drawing that the null screw 38 may be adjusted in the bobbin 26by means of the thread connection between the two.

An internally threaded collar 42 secures the cap 18 to the main housing44 which contains the modulator 12 and the servo actuator 14. Thehousing 44 is open to the force motor 10 and supports the modulator 12immediately adjacent the end of the null screw 38 with the orifice 40positioned to be controlled by the null screw.

The modulator 12 is primarily formed in a cylinder 46 which is securedin place in the housing 44 and has an annular recess 48 in its outersurface which defines a pressure chamber in which the control pressureis generated and transmitted to the servo actuator 14. The controlchamber 48 communicates through a port 50 with axial passage 52 whichterminates at the orifice 40. Thus, when the inlet 54 is connected to apressure source, either liquid or gas, the pressure in the controlchamber 48 is in turn controlled by the size of the orifice 40. It isevident that when the null screw 38 is moved away from the orifice 40 soas to effectively increase the orifice size, the pressure in the controlchamber 48 diminishes assuming that the pressure of the fluid being fedto the annular chamber 48 remains constant. Thus, the excitation of thecoil 30 of the force motor directly controls the pressure in the controlchamber 48 by varying the size of the orifice.

The servo actuator 14 is in the form of a piston 60 integrally formedwith a piston rod 62 that extends through the opening 64 in the end 66of the housing. The servo actuator 14 and more particularly its pistonrod 62 cooperates with the inner surface 78 of the housing 44 to definea bias or reference pressure chamber 80. A port 82 is provided in thehousing 44 to provide bias pressure in chamber 80, and the port 82 maybe connected to the same source of pressure source as the inlet port 54.

A number of passages 86 are formed in the cylindrical body 46. Thus, thepressure of the fluid in the control chamber 48 may be applied againstthe end surface of the servo actuator 14. The area against which thepressure may be applied on the left side of the piston 60 is equal tothe entire cross sectional area of the housing cavity, which isconsiderably greater than the area defined by the shoulder 88 exposed tothe bias pressure in chamber 80. Although the contour of the end ofpiston 60 is irregular, nevertheless its entire cross section is exposedto the pressure in chamber 48. If the pressures in the control chamber48 and reference pressure chamber is the same, it is apparent that thepiston will move to the right as viewed in the drawing because of thedifference in areas. Typically the area ratio may be a simple fractionsuch as 1:2.

The position feed back assembly 16 integral with the actuator includes apotentiometer 90 in the form of a bimetal bar 92 which extends into thecavity 94 provided in the piston rod 62 of the servo actuator 14. The

potentiometer 90 is supported by an insulation base 96 fixed to thespool body 46, and a brush assembly 98 is carried by the piston 60.Consequently, as the servo actuator 14 moves in the housing 44 under theinfluence of the differential pressure applied to the piston, the brushassembly moves along the bimetal rod 92 so as to produce a signal whichis an electrical read out of the position of the actuator. The signalmay be fed back to the signal supplied to the force motor to form asimple closed servo loop. It will be noted that leads 98 are shownconnected to the ends of the bimetal bar 92, which leads extend throughthe hole 100 formed in the cylindrical body 46 of the modulator l2, andare connected to terminal 104. The leads from the terminal 104 mayextend through an opening (not shown) in the spring support 32 andthrough the hole 36 in the pole piece 20 and exit from the unit throughthe coupling 34.

Having described the unit in detail, two typical applications of thedevice will be presented in order to afford a full understanding of theinvention. In one typical installation of the integrated servo actuatorof this invention, the device may be used to regulate the humidity of acontrolled atmosphere in a manufacturing process. Such an installationis shown in FIG. 2. The actuator piston rod 70 controls a needle valve110 in a spray system 112 for discharging water in the controlledatmosphere 1 14. The force motor is supplied a signal through anamplifier 116 from a humidity sensor 118 mounted in the atmosphere beingcontrolled. Compressed air is supplied the modulator 12 through inlet 54from a suitable source. It will be noted in the FIG. 1 that an exhaustport 102 is provided in the housing of the device to relieve pressure inthe housing to the left of the cylindrical body 46. Obviously a setpoint is established for the desired humidity, and when the humiditysensor 1 18 determines that the humidity in atmosphere 114 has deviatedfrom that set point, the signal impressed on the coil 30 of the motor ischanged so as to move the null screw 38 to vary the orifice 40 to inturn change the pressure in the control chamber 48. Consequently, thepiston 60 moves to vary the setting of the piston rod 70 to effect achange in the position of the needle valve 110 controlled by it. Whenthe humidity in the controlled atmosphere reaches the desired setting,the humidity sensor so indicates to the summing network 120, and withthe system once again in balance the actuator 14 remains stationary.

In the foregoing typical installation of the integrated servo actuator,the position feed back element 16 is not utilized. In the installationsuggested in FIG. 3 it is utilized. In this installation the unit isused to control the operation of a lathe 130 which is employed typicallyto cut a work piece 132 having a plurality of radii as suggested. Aninput signal is fed to the force motor 10, the magnitude of which iscontrolled by a patch board 134 and a sequencing switch 136. The latheis positioned by the rod 70, and the potentiometer signal is fed to thesumming network to form a closed loop to null the system when the latheis in the precise position as indicated by the feed back element 16. Inthis way precise positioning of the lathe is achieved to form thedesired radii in the work piece.

From the foregoing description it will be apparent that the device ofthis invention has numerous applications, and that modifications may bemade of the device to fit the specific application intended. Further,the configuration of the modulator may take any one of a number offorms. For example, while a modulating orifice is shown, a direct actingspool valve element could be used to achieve the same purpose. The useof such devices will provide the range of gain required of the device.

What is claimed is:

1. An integrated servo actuator comprising a housing having meansdefining an elongated passage,

a force motor assembly disposed toward one end of the housing,

a fluid modulator mounted in the passage of the housing, means fordirecting a fluid under pressure through the modulator,

a control member forming part of the force motor assembly forcontrolling the modulator,

an actuator mounted in the passage of the housing, aligned in the samedirection with the modulator, and changing position in response tochanges in the flow through the modulator,

said modulator having a surface in facing relationship to said actuator,

said actuator having means defining an elongated cavity,

and an elongated potentiometer disposed at least in part within saidelongated cavity secured to and extending from the surface of saidmodulator and operatively coupled to said actuator for producing asignal which is a function of the position of said actuator saidmodulator including at least one passage adjacent said housing forapplying pressure to one side of said actuator.

2. An integrated servo actuator as described in claim 1 furthercharacterized by an orifice forming part of the modulator, and saidcontrol member forming part of the force motor and moving to change thesize of the orifice.

3. An integrated servo actuator as described in claim 1 furthercharacterized by said modulator and control member together defining avariable orifice,

and a pressure chamber in the modulator in communication with theactuator for controlling the actuator position,

said orifice controlling the pressure in the chamber.

4. An integrated servo actuator as described in claim 1 furthercharacterized by said modulator having an inlet for a fluid pressuresource and an orifice through which the fluid discharges,

a chamber in the modulator through which the fluid flows, upstream ofthe orifice, said control member varying the size of the orifice to varythe pressure in the chamber,

said actuator including a piston slidable in the houssaid modularpassage adjacent said housing connected to the chamber for applying thechamber pressure adjacent one side of the piston,

and a biasing force exerted against the opposite side of the piston.

5. An integrated servo actuator as described in claim 1 furthercharacterized by tiometer.

8. An integrated servo actuator as described in claim 7 furthercharacterized by said elongated cavity being cylindrical in shape andlocated centrally of said actuator. 9. An integrated servo actuator asdescribed in claim 1 further characterized by said actuator having brushmeans touching said potentiometer wherein said potentiometer is movablewith reference to said brush means in response to movement of saidactuator.

1. An integrated servo actuator comprising a housing having meansdefining an elongated passage, a force motor assembly disposed towardone end of the housing, a fluid modulator mounted in the passage of thehousing, means for directing a fluid under pressure through themodulator, a control member forming part of the force motor assembly forcontrolling the modulator, an actuator mounted in the passage of thehousing, aligned in the same direction with the modulator, and changingposition in response to changes in the flow through the modulator, saidmodulator having a suRface in facing relationship to said actuator, saidactuator having means defining an elongated cavity, and an elongatedpotentiometer disposed at least in part within said elongated cavitysecured to and extending from the surface of said modulator andoperatively coupled to said actuator for producing a signal which is afunction of the position of said actuator said modulator including atleast one passage adjacent said housing for applying pressure to oneside of said actuator.
 1. An integrated servo actuator comprising ahousing having means defining an elongated passage, a force motorassembly disposed toward one end of the housing, a fluid modulatormounted in the passage of the housing, means for directing a fluid underpressure through the modulator, a control member forming part of theforce motor assembly for controlling the modulator, an actuator mountedin the passage of the housing, aligned in the same direction with themodulator, and changing position in response to changes in the flowthrough the modulator, said modulator having a suRface in facingrelationship to said actuator, said actuator having means defining anelongated cavity, and an elongated potentiometer disposed at least inpart within said elongated cavity secured to and extending from thesurface of said modulator and operatively coupled to said actuator forproducing a signal which is a function of the position of said actuatorsaid modulator including at least one passage adjacent said housing forapplying pressure to one side of said actuator.
 2. An integrated servoactuator as described in claim 1 further characterized by an orificeforming part of the modulator, and said control member forming part ofthe force motor and moving to change the size of the orifice.
 3. Anintegrated servo actuator as described in claim 1 further characterizedby said modulator and control member together defining a variableorifice, and a pressure chamber in the modulator in communication withthe actuator for controlling the actuator position, said orificecontrolling the pressure in the chamber.
 4. An integrated servo actuatoras described in claim 1 further characterized by said modulator havingan inlet for a fluid pressure source and an orifice through which thefluid discharges, a chamber in the modulator through which the fluidflows, upstream of the orifice, said control member varying the size ofthe orifice to vary the pressure in the chamber, said actuator includinga piston slidable in the housing, said modular passage adjacent saidhousing connected to the chamber for applying the chamber pressureadjacent one side of the piston, and a biasing force exerted against theopposite side of the piston.
 5. An integrated servo actuator asdescribed in claim 1 further characterized by said potentiometercomprising a metal bar, and a circuit including brushes in contact withthe bar.
 6. An integrated servo actuator as described in claim 4 furthercharacterized by said force motor including a movable coil member andfixed pole pieces, said coil member carrying the control member to varythe orifice size.
 7. An integrated servo actuator as described in claim1 further characterized by said modulator including means defining apassage for accommodating a pair of wires of said potentiometer.
 8. Anintegrated servo actuator as described in claim 7 further characterizedby said elongated cavity being cylindrical in shape and locatedcentrally of said actuator.